2023 Prius Ltd. - Goes to Accessory Mode instead of Ready

when you step on the brake, do the brake lights come on?

search for the 12v battery draining threads, there are a couple of them, might be the prime though, i'm not sure

 

My bet is your battery is bad, even if the dealer said it checks out okay.

 

My understanding is that if it's a bad 12v battery (still to be determined for my case, although I did get a new 12v battery replacement), the battery is the same in the Prime as in the standard Prius models. As far as the failure to enter READY state, that can be a symptom of a low 12v battery, as I experienced that once. On the last failure to start before the 12v battery heads for a terminal loss of charge, the brake pedal may start with pressure, but will quickly lose pressure and loudly shudder – like an ABS trigger, but much stronger and at the early part of the brake pedal travel.

My charging system in my 2024 Prime has no documented issues (both from my experience and from days of dealership service department testing), so that almost completely rules out the charging system failure that affected a small number of 2023 Primes, but confirms the plausibility of bad 12v batteries out there that should affect Prime and non-Prime models similarly.

 

You may find this interesting. I own a 2023 Prius Prime XSE. Last year I went on vacation for 13 days and returned to a dead battery. I didn't think that a 13 day/night hiatus in the early summer should result in a flat out dead battery, so I took it into the dealership. They ran some tests and told me everything was perfectly fine, and that I shouldn't expect the battery to maintain charge for that length of time (which I find to be completely ridiculous and totally unreasonable).

In any case I left with nothing done to the car. Then about 6 months later the battery went dead on me again when the overnight temperature dipped to 40 degrees. This time I called the service manager and told him they were to keep the car as long as needed to figure out what was wrong, and that I didn't want it back until the problem was fixed and the 12V battery was replaced. He was very noncommittal on the last point. The dealership kept the car for 4 days while they ran tests under the supervision of Toyota regional. (They gave me a loaner). The final result was they claimed there was a software bug that kept the computer trying to ping Toyota's servers that was causing the problem. They advised me to delete the app on my phone and install the newest update because otherwise the same defective software would run again (which is odd because I had deleted the app once the free service expired months earlier). They also replaced the 12V battery. I am dubious that this has actually resolved the problem, but I'll know in the next six months.

Assuming that what they told me was true then Toyota should issue a recall notice for every single car made when mine was. They haven't, which I find a bit concerning and puzzling. In any case, it pays to be very insistent with the dealer and Toyota that such problems are neither 'normal' nor acceptable, but rather design defects that absolutely must be resolved by them.

 

Fight the good fight Brother!

"Oh, your phone's old app is allowing the car to run the battery down to DEAD.", (which, btw, is very harmful to any lead acid battery. )
What a strange thing to have a dealership tell you.

As you said, this should be common knowledge to owners.
Or better yet, design the car to NEVER run the 12V battery down to DEAD.
Load Shed, turn off RF receivers at some point to maintain enough power to remain in the battery to boot up the car.
This is not Rocket Surgery, just a simple SW update.